(CNN) -- The deaths of six U.S. soldiers in Afghanistan are being tied, directly or indirectly, to the search for Army Sgt. Bowe Bergdahl after he went missing and was captured by the Taliban in 2009, former unit members allege.
The former soldiers' controversial accusations come days after Bergdahl was released after almost five years of enemy captivity.
A U.S. official told CNN that Pentagon and Army officials have looked at the claims, and "right now there is no evidence to back that up."
Asked about the debate, Defense Secretary Chuck Hagel told reporters Wednesday that he did not know of specific circumstances or details of soldiers allegedly dying as a result of the efforts to find Bergdahl.
It is also "unfair" to Bergdahl and his family to presume anything about his motivations for leaving the base, Hagel said. He stressed that the Army would conduct a review of the case.
Former Army Sgt. Evan Buetow, Bergdahl's former team leader, elaborated on the accusations. "I can't say for a fact and I don't know if there is really anyone who can prove that soldiers died on a directed mission to find Bergdahl. However, every mission, especially in the following two or more months -- those were directed missions," he told CNN's Jake Tapper. "Everything after that, they were still missions that were in search of Bergdahl."
Here's a look at those six fallen soldiers.
2nd Lt. Darryn Deen Andrews
Andrews was killed in September 2009 when enemy forces attacked his vehicle with a roadside bomb and a rocket-propelled grenade in the Yahya Khel district of Paktika province, Afghanistan. The Dallas, Texas, native was 34.
Andrews' mother, who still wears her son's ID tags, spoke to KHOU this week. The CNN affiliate reported Andrews died using his body to shield two other soldiers from a blast.
Sondra Andrews feels her son was killed trying to save a "traitor."
"My son's life was worth more than that," she told KHOU.
Staff Sgt. Clayton Patrick Bowen
Staff Sgt. Clayton Patrick Bowen was a 12-year Army veteran who had served as a drill sergeant and shooting instructor before being shipped out to Afghanistan in February 2009, according to a U.S. Army account of his service.
The 29-year-old San Antonio, Texas, man was traveling to provide security for Afghanistan's presidential elections when his vehicle hit a roadside bomb on August 18, 2009, according to the Army account.
He and another soldier, Pfc. Morris Lewis Walker, died.
Bowen, who joined the Army straight out of high school, served as a member of the 82nd Airborne Division's All-American Chorus before deploying to Afghanistan with the 501st Infantry Regiment. He also was featured as the cover model for a book on how to survive basic combat training, the Army account quoted his mother, Reesa Doebbler, as saying.
"Clay had a sense of humor second to none and lit up a room when he walked in," Doebbler said in a 2010 CNN iReport.
Pfc. Morris Lewis Walker
Walker died at age 23 when a roadside bomb exploded as he traveled through Afghanistan's Dila district. He died alongside Staff Sgt. Bowen on a mission to provide security for Afghanistan's presidential elections, according to the Army.
Walker joined the Army in 2008 after attending the University of North Carolina, where he played on the basketball team, according to a UNC memorial web page.
"If you got to spend time with Mo Walker, you remembered it," the student newspaper, The Daily Tar Heel, quoted former student Sam Rosenthal as saying. "He had a charisma and a warmth that just rubbed off and also a pride and a sense about himself. I had never met anybody with so much confidence and even borderline arrogance that never rubbed people the wrong way."
Staff Sgt. Kurt Robert Curtiss
Curtiss joined the Army the day after the 9/11 attack, according to CNN affiliate KSL.
He was shot to death during a firefight in which his unit was supporting Afghan security forces in Paktika province on August 26, 2009.
The Murray, Utah, man died during what the Army called a clearing operation at a hospital at a medical clinic in Sar Hawza.
He was a well-regarded squad leader whose leadership style engendered fierce loyalty in at least one soldier -- the squad member who faced an onslaught of enemy fire in an effort to rescue him, the Army said in a 2009 article about two soldiers awarded the Silver Star for actions during the firefight.
"When I first got here, he showed me everything," the Army piece quoted one of those soldiers, Spec. Robert Parson, as saying. "Just small things that only a veteran would know."
He left behind a wife, two small children, and a humorous reputation, his mother, Ruth Serrano, told KSL.
"He was quite the joker," she said. "He could cheer up anybody."
Pfc. Matthew Michael Martinek
Martinek died September 11, 2009, at Landstuhl Regional Medical Center in Landstuhl, Germany, of injuries suffered from an attack about a week earlier in Afghanistan.
Enemy forces attacked his vehicle with a roadside bomb, a rocket-propelled grenade and small-arms fire in Paktika province.
His mother spoke to CNN affiliate KTUU, praising her son's sacrifice. Martinek was sent to Afghanistan during the first quarter of 2009, the station said.
"What we hope will not be lost on the American people is the true heroism of the soldiers who risked their safety to relentlessly attempt to rescue Bowe," said Cheryl Brandes. "One of those brave men was our son and brother Matthew Martinek."
Martinek, 20, was a native of DeKalb, Illinois.
Staff Sgt. Michael Chance Murphrey
Murphrey was killed in September 2009 when forces attacked his unit with a roadside bomb in Paktika province.
A native of Snyder, Texas, he was 25.
According to an online obituary, Murphrey decided he wanted to be an Army paratrooper when his family took him skydiving on his 17th birthday. He loved to hunt, hike, camp and fish.
Murphrey was survived by his wife and two young children, a son and daughter.